The present invention is directed to electrical switches suitable for application in a low voltage alternating current (600 V max) electrical distribution systems, such as for example 120 volts 60 Hz systems having a rated capacity of up to approximately 800 Amperes per pole.
So-called "knife blade" rotary and linear "quick-break" electrical switches in fused or unfused form are known in the electrical distribution industry. Respective examples of each type of switches are shown in U.S. Pat. Nos. 5,053,590 and 5,072,081. With respect to rotary switches, one or more pivotally mounted blades are pivotable from an open position to a closed position which enables electrical continuity from a line side of the switch to a load side of the switch. When the switch is in a closed position, the knife-blade establishes electrical continuity with a line strap. The strap also often includes one or more contact clips, comprising a strip of bent conductive metal. When in a closed position, the blade establishes biased contact with the line strap clip, in order to enable good electrical continuity.
Prior art knife-blade rotary and linear switch contacts can tend to weaken contact pressure between the blade and strap as the switch contact surfaces become warm. It would be desirable to maintain relatively constant contact pressure between electrical switch blades and line straps over the life of the switch. Another problem with existing and known knife-blade type electrical switches is that the pivoting side of the blade must also maintain good electrical continuity with a strap located attached thereto. In the past, in order to maintain such a conductivity between the strap proximal the pivot point and the blade structure it was necessary to construct a switch with a very tight fit. While the tight fitting pivot were ensured good electrical continuity, it would increase the physical effort necessary to pivot the switch blades from the on or closed to the off or open positions. Continuity of the pivot side of the blades could also possibly weaken due to wear in the switch.
It is an object of the present invention to create an electrical switch that maintains relatively constant blade and strap pressure even as the switch contact points wear during normal service life.
It is also an object of the present invention to create an electrical switch which maintains bias pressure on the pivoting side of the blades into contact with a respective line strap when the switch is in the closed or on position, yet which decreases the respective biasing pressure when the switch is being translated to the open or off position.